1. Field of Invention
The invention relates to the field of polishing pad seasoning, and in particular to the seasoning of hydrophobic semiconductor polishing pads used in the planarization of semiconductor substrates.
2. Description of Related Art
Chemical mechanical polishing (CMP) or planarization is a technique whereby surfaces, such as semiconductor substrate surfaces, are planarized by the simultaneous application of both a chemical etching and a mechanical polishing process. Planarization is typically used to globally planarize surfaces such as the upper surface of a semiconductor wafer. The wafer is typically held upon a carrier surface by any suitable means and is rotated with respect to a polishing pad. A polishing slurry containing abrasive particles, an etchant and/or other suitable polishing materials is introduced between the polishing pad and the surface of the semiconductor wafer that is to be planarized. The combination of the mechanical polishing and the etchant results in the exposed surfaces of the wafer being removed by the process.
Most commercially available polishing pads are comprised of hydrophobic materials. These substances include polyurethanes, amines, organic polymers, and resins. Planarizing pads are usually composed of polyurethane. Polyurethane is typically utilized because urethane chemistry allows the pad characteristics to be tailored to meet specific mechanical properties.
Before being employed in planarization, such polishing pads must be seasoned or conditioned, i.e., broken in. If the polishing pads are used in planarization without first being seasoned, many problems result. One of the main problems is that the polishing pads, being hydrophobic, do not initially or readily wet with the polishing solution added in the planarization procedure. This results in uneven distribution of the polishing solution, and therefore uneven polishing of the wafer surface, and may also result in scratching of the surface of a significant number of wafers. An uneven or scratched wafer is not useable in the manufacture of semiconductors as such results in damage to the devices and structures formed on the semiconductor wafer.
Several techniques are known in the art to attempt to address the problems created by using hydrophobic polishing pads. For example, U.S. Pat. No. 5,547,417 describes a method of polishing a thin film formed on a semiconductor substrate. During polishing, the polishing pad is continually conditioned by forming a plurality of grooves into the polishing pad. The grooves are formed by a conditioning block having a substantially planar bottom surface with a plurality of groove generating points extending from the substantially planar surface of the conditioning block. The grooves are generated by sweeping and rotating the conditioning block between an outer radius and an inner radius of the polishing pad.
U.S. Pat. No. 6,126,532 describes a polishing pad for polishing a semiconductor wafer that includes an open-celled, porous substrate having sintered particles of synthetic resin. The porous substrate is a uniform, continuous and tortuous interconnected network of capillary passages. The pores of the porous substrate have an average pore diameter of from about 5 to about 100 microns that enhances pad polishing performance. It is described that the polishing pad is conditioned before use according to a buffing method that mechanically conditions the top pad surface and converts the top pad surface from hydrophobic to hydrophilic.
Such mechanical seasoning methods are typical in the art. However, these methods require both time and additional processing steps, and thus are expensive to perform. For example, a method for breaking in new polishing pads might typically comprise laying the new polishing pads, subjecting the pads to a water brush, then to a polishing slurry brush, and then followed by several to many hours of dummy wafer runs, before employing the polishing pads to polish prime production wafers. Moreover, the occurrences of polishing scratches and haze, and thus yield loss, even after such mechanical seasoning of the polishing pads, can remain high for many hours or days.
U.S. Pat. No. 6,200,901 describes methods of oxidizing the surface of a photoresist material on a semiconductor substrate to alter the photoresist material surface to be substantially hydrophilic. Oxidation of the photoresist material surface substantially reduces or eliminates initial sticking between a planarizing pad and the photoresist material surface during chemical mechanical planarization. This oxidation of the photoresist material may be achieved by oxygen plasma etching or ashing, by immersing the semiconductor substrate in a bath containing an oxidizing agent, or by the addition of an oxidizing agent to the chemical slurry used during planarization of the resist material. This patent thus describes altering the wafer surface to assist in planarization.
U.S. Pat. Nos. 5,990,012 and 6,277,015 describe a method of chemical-mechanical polishing of a surface of a semiconductor substrate by providing a fixed-abrasive polishing pad; providing a surface to be polished; and providing a chemical polishing solution containing a surface tension-lowering agent that lowers the surface tension of the solution from the nominal surface tension of water to a surface tension that sufficiently wets a hydrophobic surface to be polished such that chemical-mechanical polishing is accomplished. The patents also describe pad improvements that mechanically sweep the polishing solution under the pad or that receive polishing solution from the back of the pad such that a tangential and radial shear is placed on the polishing solution as it flows away from the pad. These patents thus focus on the composition of the polishing solution.
U.S. Pat. No. 6,364,749 describes an improved CMP polishing member having a plurality of protrusions with an outer surface, the outer surface of the protrusions defining a polishing surface of the CMP pad adapted to polish or planarize an exposed surface of a semiconductor wafer. A plurality of cavities interposed between the protrusions and the cavities have a hydrophilic surface so as to attract wetting solution to thereby enhance retention of the wetting solution adjacent the polishing interface between the surface of the semiconductor wafer and the polishing surface of the polishing pad. In one embodiment, the protrusions are comprised of a fixed abrasive material, such that the polishing pad is a fixed abrasive polishing pad. In another embodiment, the cavities between the protrusions are coated with a hydrophilic material so as to retain wetting solution immediately adjacent the exposed surfaces of the fixed abrasive protrusion. The protrusions can either be in the form of a plurality of discrete protrusions formed on a first surface of a substrate of a semiconductor wafer or, alternatively, can be comprised of a plurality of spiral protrusions.
What is still desired is a simplified method for seasoning new hydrophobic polishing pads prior to use in planarizing semiconductor wafers, which method renders at least the polishing surface of polishing pad hydrophilic so as to improve polishing and reduce polished semiconductor substrate yield loss, and which method is less time consuming and less expensive than conventional mechanical seasoning methods.
In a first aspect of the present invention, the invention relates to a method of preparing a polishing pad comprised of a hydrophobic material for a polishing procedure, comprising, prior to the polishing procedure, contacting the polishing pad with a solution comprised of at least one component for converting at least a portion of a polishing surface of the polishing pad from hydrophobic to hydrophilic, and maintaining the polishing pad in a wet state between the contacting step and the polishing procedure.
In a further aspect of the present invention, the invention relates to a method of planarizing a semiconductor substrate surface, comprising seasoning an unseasoned polishing pad comprised of a hydrophobic material by contacting the polishing pad with a solution comprised of at least one component for converting at least a portion of a polishing surface of the polishing pad from hydrophobic to hydrophilic to derive a seasoned polishing pad, maintaining the seasoned polishing pad in a wet state following the seasoning step and before contacting the seasoned polishing pad with a surface of a semiconductor substrate, and contacting the seasoned polishing pad with a surface of a semiconductor substrate to be planarized in the presence of a polishing composition to thereby planarize the semiconductor substrate surface.